The flocculation of matter suspended in water to enhance clarification rates is an important aspect of industrial and municipal water treatment. Inorganic coagulants such as lime, alum, ferric chloride, ferrous sulfate, ferric sulfate and sodium aluminate have traditionally been used. These chemicals, while aiding in the removal of suspended solids, generally provide additional quantities of dissolved inorganic solids which can themselves provide water problems, particularly where the water is recirculated in substantial quantities.
Certain polymeric organic coagulants have also proved valuable for flocculation. These polyelectrolytes are often preferred because, in addition to their minimal effect on dissolved solids, they tend to produce less, more compact waste sludge, and they tend not to appreciably affect the pH of the treated water. Cationic polyamines are common commercially available organic coagulants. In addition, high molecular weight polymers such as anionic polyacrylamides have been used to aid in flocculation achieved with primary organic or inorganic coagulants. Anionic polymers are often used in combination with primary organic or inorganic coagulants and aluminum or iron salts to aid in flocculation.
The detackification of sticky materials in aqueous systems is another common problem in many industrial operations. For example, in a commercial paint spraying operation which is performed in a spray painting booth, less than half of the paint used actually coats the surface to be painted, with the remainder representing overspray. The overspray is removed from the paint spray booth by air currents which are scrubbed by recirculating water. The oversprayed paint particles become entrained in the spray booth water which, if untreated, may cause plugging of piping and spray nozzles thus reducing the operating efficiency of the spray booth and increasing the voc emissions. In the spray application of solvent based paints such as polyurethanes, epoxy resins, lacquers, enamels, as well as waterborne paints, it is normally necessary to trap the oversprayed coating materials in some way to avoid their building up on the walls and exhaust system surfaces of the spray booth. In many large industrial installations, including especially auto body painting systems, oversprayed coating materials are collected in water curtains which cascade down the interior spray booth walls. The agglomeration and accumulation of live coating material in the water supply of these systems results in serious problems, such as blockage of the pipes and pumps which circulate the water, and a build-up of paint on the walls of the booth beyond the water curtain. As more and more coating material is sprayed in the booth, the material removed from the air builds up in the water in the form of a tar-like coherent sludge which in a short time can foul the pumps and lines of the paint spray booth recirculating water system. Furthermore, this sludge is extremely difficult to remove from the pump, lines, reservoir, and other internal surfaces of the system with which it comes in contact. The accumulation of coating materials in the bottom of the water reservoir also creates a serious problem when the system is periodically cleaned out, with much effort being required to remove the heavy build-up of coating material on the bottom of the reservoir. Many present paint spray booth detackification treatments are based upon clays (e.g. hectorite or bentonite), amphoteric metals (e.g. sodium zincate) and polymers (e.g. diallyldimethyl ammonium chloride and melamine aldehydes) or a combination of these.
While the majority of paints currently used in the market are organic solvent based, in an attempt to lower VOC emissions from the painting operation, the use of waterborne coatings is becoming increasingly more common. Waterborne paints are resin suspensions stabilized by a surfactant matrix which upon incorporation into the paint spray booth water disperse and/or emulsify resulting in an increase in both suspended and dissolved solids. While these solids must be coagulated and removed from the spray booth water in order to maintain an effective painting operation, these solids do not require detackification as required by organic solvent based paints. These paint solids require agglomeration for effective removal from the system.
There are, however, some paint spray booth operations wherein both organic solvent based paints and waterborne paints are sprayed into the same booth. Due to major differences in the formulations of waterborne paints and solvent based paints, separate paint detackification agents have heretofore been necessary to treat the respective paint particles in the spray booth water. Consequently it would represent a major benefit if a single water treating agent could act not only as a coagulant but could also act as a detackifier or optionally if the coagulant could be used in combination with a detackifier without decreasing the performance of the detackifier.
Various inorganic compounds have been used as flocculating and coagulating agents in paint spray booth water treatment systems.
More specifically, coagulation involves the addition of a cationic material which reduces the negative zeta potential of a particle. This results in agglomeration of two particles or more, providing a pin floc. All coagulants are typically cationic in their operation pH range.
Detackification involves the adsorption of the material added to a paint particle (as disclosed in this invention) similar to a coagulant. However, not all detackifiers are recognized as coagulants. For example, inorganic clays are detackifiers but they do not perform as coagulants. This is because they do not have overall cationic charge and therefore do not agglomerate particles, which generally have a negative charge.
In addition, not all coagulants are effective detackifiers, since a detackifier after adsorption to the paint particle must render the paint non-sticky. Addition of inorganic coagulants such as alum or organic polymeric coagulants, such as DMA-EPI's, do not provide a non-tacky paint.
Flocculation is the briding of pin flocs (which are 2 or more particles, doublets, agglomerated or coalesced by a coagulant). The effective range of this bridging is much greater than a coagulant because the molecular weight of the material is 2-3 orders of magnitude greater. Reduction of the surface charge of the particle, zeta potential, is also not as important as with a coagulant. As a result, flocculants can be anionic or nonionic in addition to cationic.
For example, aluminum sulfate, also known in the trade as alum, has been used extensively as a coagulant in paint spray booth water. However, the use of inorganic treating agents have numerous disadvantages, in particular they produce high volumes of residual waste sludge. Furthermore, none of the inorganic treating agents are effective for detackifying a broad range of solvent paints. It is, therefore, desirable to treat the water in the booth in such a way as to render the oversprayed coating material free of stickiness and tackiness so that it will readily separate itself from the water, not adhere to the curtain walls, pipes, pumps and other internals of the spray booth system. It is also desirable to coagulate the paint particles to form a detackified floating sludge.
One approach to detackification has been to combine certain polymeric materials with amphoteric metals. Thus, for example, U.S. Pat. No. 3,861,887 discloses treatment of paint booth wash water with a blend of polycationic water dispersible polymer with a water-soluble salt of an amphoteric metal to reduce the tackiness of paint. One problem with this approach is that use of metals, such as zinc, can create additional disposal concerns for the wastewater and sludge recovered from it.
Another approach has been to use clay-based treatment. For example, U.S. Pat. No. 4,504,395 discloses that certain hectorite clays can be effectively used to detackify oversprayed paint. A problem with this approach is that the sludge produced using clays can be difficult to dewater, resulting in larger volumes of potentially hazardous materials requiring haul-out to a secure landfill.
Another industrial process which experiences problems with sticky materials in aqueous systems is a pulp and papermaking system which uses a pulp suspension derived from natural cellulosic fibers containing pitch particles and/or recycled pulp containing residual ink, adhesives, anionic trash, etc. These sticky materials adhere to the pulp and paper making equipment resulting in sticky deposits which negatively affect the operation of the paper making equipment. One approach to this problem has been the use of pulp additives such as anionic aryl sulfonic acid-formaldehyde condensates or cationic dicyandiamide-formaldehyde condensates. However, there remains a need for effective treatment agents which detackify sticky material in industrial aqueous systems, such as paint overspray particles, pitch and stickies in papermaking systems, etc.
Yet another problem in industrial aqueous systems is the treatment of wastewater streams containing emulsified oil, i.e. oil-in-water emulsions. Inorganic coagulants alone or in combination with organic polyelectrolytes have been used in demulsification. However, these treatments are not completely satisfactory because they increase solids content, which can cause waste stream disposal problems.
Tannins occur naturally in various vegetative materials including barks and woods. Established industrial practices of extracting tannins from the wood of the quebracho tree and the bark of the wattle tree have made condensed tannins available in substantial quantities. Condensed tannins are polyphenolic and polymerize in combination with other chemicals such as formaldehyde. A. Pizzi, in "Condensed Tannins for Adhesives" Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 359-369 discusses natural tannins and their particular use in the manufacture of particle board, plywood, and other industrial products which incorporate adhesives.
British Pat. No. 899,721 discloses use of a reaction product of a tannin, a formaldehyde and an amino or ammonium compound in the flocculation of suspensions such as sewage, industrial waste, and natural water. The disclosed advantages of using these flocculants are that they do not affect the pH of the suspension and that they do not affect the dissolved inorganic solids content of the treated water.
U.S. Pat. No. 4,558,080 discloses the production of stable tannin-based flocculants made by polymerizing tannin with an aldehyde (e.g. formaldehyde) and an amino compound (e.g. monoethanolamine) while monitoring the viscosity of the reacting mixture.
U.S. Pat. No. 4,734,216 discloses a flocculating composition comprising the polymerized tannin described in U.S. Pat. No. 4,558,080 in combination with an inorganic flocculant such as aluminum sulfate or iron chloride.
U.S. Pat. No. 4,948,513 discloses a method for detackifying spray booth water using a composition comprising the polymerized tannin of U.S. Pat. No. 4,558,080 in combination with a hydrophillic-lipophillic copolymer and/or a diallyl dimethyl ammonium chloride polymer.
U.S. Pat. No. 4,944,812 discloses aqueous solutions of the reaction product of a vegetable tannin, an aldehyde (e.g. formaldehyde), and an amine, (e.g. diethanol amine) for the treatment of metals to enhance corrosion resistance.
U.S. Pat. No. 5,256,304 discloses the reaction product of a tannin, diallyl dimethyl ammonium chloride (DADMAC) and an aldehyde for use in removing metal ions from oil waste waters by demulsification and flocculation.
European Publication No. 630,858 discloses a water soluble or dispersible tannin containing polymer composition having the formula EQU Tannin-[N-C-A]
for water clarification. The N-C-A moiety represents polymer comprised of monomers N, C, and A. N represents a nonionic monomer, C represents a cationic monomer, and A represents an anionic monomer, with monomers N and C being optional. The preferred cationic monomer C is dimethylaminoethyl acrylate. Allyl and ethoxylated allyl ethers of polyalkylene glycol are disclosed as a suitable nonionic monomers. All polymerization appears to occur through free radical initiation of the double bond.
While these tannins have been used as described to treat industrial aqueous systems, the search has continued for ways to increase the efficiency of flocculation and clarification while reducing material consumption and other costs.